You are already doing the most important thing you can do — and that is praying for your husband. Only God can open his eyes to the truth of the Gospel, and only God can convict him of his need for Christ’s forgiveness.
Don’t give up; over the years I have received numerous letters from wives (and husbands) who have prayed for their spouse for many years, and eventually seen them turn to Christ. When your husband was young, the “seed” of the Gospel may well have been planted in his heart through his family. God has also used your example to plant those same seeds within him. But seeds take time to sprout, and sometimes they only come to life after much time has passed.
In addition, ask God to help you be an example to him of what it means to have Christ living in your heart. I often think of Paul’s words to women who were married to unbelieving spouses: “If any of them do not believe the word (of the Gospel), they may be won over without words by the behavior of their wives” (1 Peter 3:1). Does your husband see Christ’s love and peace and patience at work in your life?
Finally, don’t let your husband’s indifference keep you from serving Christ or being active in your church. God wants to use you, not only in his life but in the lives of others as well.